1. Field of the Invention
The invention relates to a pipe coupler for use in coated pipe-lines, more particularly a branch connection provided with an insulating coating for the main pipe ends of insulated pipe-lines of plastics.
2. Description of the Prior Art
Insulated pipe-lines are used, for example, for carrying hot water for district heating and consist of a pipe-line for the fluid to be conveyed, with larger diameter tubular casings disposed concentrically around said pipe-line, the space between the pipe ends of the pipe-line and the tubular casing being filled with insulating material, more particularly a foam material.
If a pipe end has to be provided with a branch connection, a branch pipe is welded to said pipe end and thus the latter will be devoid of insulating material and a tubular casing at a place where it is connected to the branch pipe. A shell is then disposed around the whole system, insulating material (e.g. foam) being present in this shell. A pipe connection of this kind is described, for example, in Dutch Patent application No. 8100776, being not a prior publication. A good connection is obtained in fitting a branch pipe to a pipe end by welding the branch pipe directly to a pipe end of a pipe-line.
However, due to temperature effects the pipe end may shift longitudinally with respect to the tubular casing. As the branch pipe cannot shift laterally in view of the insulating material, the weld between the branch pipe and the pipe end is undesirably subjected to loading.